If you’re relaxing as you peruse this, the subsequent sentence may frighten you sit-less: “Perching is the modern smoking; it’s just as hidden,” cautions Marc Hamilton, Ph.D., a biology and biochemistry professor at the University of Houston.
Hamilton is emphasizing how countless Americans are allowing their leg muscles — and consequently their bodies — to deteriorate. “You’ve witnessed the flat line on an EKG when all the physicians hurry in? That’s precisely what’s happening to your leg muscles when you’re perched,” he adds. While he articulates this, I flashback to a position I once held at a digital agency: I arrived on my initial workday at the New York City office to discover that half the personnel were standing at their computers. This was because they lacked chairs. The office primarily consisted of makeshift desks about waist-high that we would convene at, similar to bar tables. (More: 3 Essential Exercises to Counteract a Sedentary Job Physique)
As it turns out, my hipster colleagues were onto something. “Standing while conversing on the telephone or organizing paperwork isn’t physical activity by anyone’s standards, nonetheless, compared to sitting, it slightly elevates your metabolic rate,” explains Hamilton. If you were curious, performing “light office work” while seated burns 96 calories per hour for an average 140-pound woman in contrast to 147 calories while standing, according to a widely accepted compilation of physical activity. Nonetheless, “when we’re seated for lengthy periods, numerous ‘negative’ genes are activated, including those that prompt muscle wasting,” adds Hamilton. (See also: 5 Approaches to Develop More Robust, Larger Gluteal Muscles That Have Nothing to Do with Squats)
Intrigued, I make my way to the Kaiser Permanente Los Angeles Medical Center to personally witness the consequences of selecting a chair and a laptop for the entire day on my leg muscles. Once there, Barry R. Chi, M.D., head of physical medicine and rehabilitation, connects my leg muscles to surface electrodes that are connected to an electromyography (EMG) machine through several lengthy cables. I recreate a typical day for my legs by sitting, standing, walking (both in heels and flats), rising onto tiptoes, and jogging. To gauge everyday muscle activity, we conclude with squats and lunges.
True to the EKG comparison, the leg muscle readings on the EMG monitor are indeed flat lines when I am seated — it appears as if I’m nonexistent. However, something changes when I rise in front of the monitor: it fills with electrical activity. “You may not perceive anything, but your leg muscles are now supporting your entire body weight, and all of the major muscles of the body are currently involved in static contractions,” states Dr.
Chi, indicating the raised lines. “Remaining on one’s feet for two hours can be tantamount to engaging in a two-mile jog,” he clarifies.
Interestingly, when I perch or stroll in high heels, my quadriceps and hamstrings exhibit greater surges than when I’m in flats, but Dr. Chi quickly cautions against long-term ramifications of wearing heels, such as back pain.
How Genetics Modify Your Leg Muscles
The length of your lower limbs is essentially a matter of genetics — and this could imply way, way back in the family tree. In general, women are marginally leggier than men: The latest body-measurement statistics from a SizeUSA study, conducted by TC², a not-for-profit apparel industry resource, reveal that the typical 18- to 45-year-old woman’s legs (determined by crotch height) constitute approximately 45 percent of her overall height compared to 44 percent for the typical man in the same age group. (More: Is It Actually More Challenging to Shed Pounds When You’re Short?)
Leg muscles, on the other hand, tell a different tale. They heavily rely on your genes and what you do with them. The latter portion of that equation will be discussed later — that is, diet, exercise, couch-sitting habits — but for now, let’s engage in a swift lesson on leg muscle anatomy.
Every individual possesses the same main leg muscles: quadriceps, hamstrings, adductors, shins, and calves. However, within those larger muscle groups, there exist numerous smaller muscles, each with their own distinct function(s) — adduction, flexion, extension, rotation. For instance, the semitendinosus, semimembranosus, and biceps femoris all form part of the hamstrings. It’s worth noting that while adductor muscles are situated on the inner thigh and aid in moving your leg toward the center of your body, abductors are not solely “outer thigh” muscles, but rather muscles located in the glutes that facilitate hip rotation. This narrative will focus on the muscles beneath the buttocks. (But here’s a guide to your buttock muscles if you’re interested.)
Yet, there exists a vast array of sizes and muscle composition among individuals where even experts engage in debate. “Muscle fibers in humans evolved so that most of us possess leg anatomy primarily composed of slow-twitch fibers, which provide us with endurance during long-distance runs,” states Daniel Lieberman, Ph.D., professor of human evolutionary biology at Harvard University. “We are built more for stamina, whereas chimpanzees exhibit greater concentrations of fast-twitch fibers,” he elucidates. With fewer dominating fast-twitch fibers, humans find themselves at a disadvantage when it comes to velocity. “As a species, we are subpar sprinters,” says Lieberman. “Cheetahs can sprint at 25 meters per second. The fastest human, Usain Bolt, runs only 10.4 meters per second,” he adds. (See also: Everything to Know About Slow- and Fast-Twitch Muscle Fibers)
It turns out that the quadriceps, or quads, are the real unpredictable element of your leg muscles, as they can vary from predominantly fast-twitch to the complete opposite: The quads of someone like Bolt can contain up to 90 percent fast-twitch fibers, says John P. McCarthy, Ph.D., former professor of physical therapy at the University of Alabama at Birmingham. On the other hand, elite marathoners’ muscles can contain up to 90 percent slow-twitch fibers. The quads of average individuals, or even those of swimsuit models or large bodybuilders, are more a fifty-fifty combination of the two.
The issue is that many individuals are often so afraid of developing bulky thighs and calves that they overlook to strength-train their legs. However, in reality, bulky legs are primarily due to fat. “Our legs can transition from thin meat to marbled rump roast without our knowledge,” says Vonda Wright, M.D., a double board-certified orthopedic surgeon based in Orlando, Florida. “It’s a snowball effect when we start accumulating fat, and it impacts the function and strength of muscle,” she continues. (See: Ignite Your Lower Body with This Workout Suitable for Beginners)
Composition of Your Leg Muscles
If you were assigned female at birth, your hormones have been signaling fat cells to be stored around your buttocks and thighs since puberty, ultimately to help serve as reserve energy for pregnancy and breastfeeding. “Women tend to gain fat in very specific body parts, mostly those from the waist to the knee,” explains Andrew Da Lio, M.D., professor and chief of plastic and reconstructive surgery at the University of California, Los Angeles. The most common of those parts is the outer thigh, he says.
There are two levels of fat in the legs: a surface layer and a deeper layer, explains Dr. Da Lio. The surface layer is where you’d find cellulite when fat pushes through between the tissues that connect the skin to the underlying muscle. Gain too much of the deeper leg fat and it can actually start infiltrating your leg muscles, says Dr. Wright. The good news? This deeper layer is also usually the initial layer of fat to shrink when you exercise. (For more: Try This Leg Workout Without Any Equipment When You Can’t Make It to the Gym)
How to Strengthen Your Leg Muscles
Last fall, with the assistance of the UCLA Center for Human Nutrition’s Risk Factor Obesity Program lab, I conducted an experiment. I performed every exercise I routinely avoid in the hope that it would make my legs resemble Schwarzenegger’s: numerous squats and lunges each week combined with the stair climber and cycling classes.
And an amusing incident occurred: I misplaced 10 percent of the adipose tissue from every thigh within a span of four weeks, as per the laboratory’s DEXA (dual-energy X-ray absorptiometry) body scanner. At the end of eight weeks, during which I also adhered to a low-calorie diet, I had shed over an inch from each thigh.
You have the ability to alter the structure of your leg muscles — the proportion of fat to lean mass. Enhancing your power and stamina will result in a transformation in the appearance of your legs,” declares Dr. Wright. And there was my evidence in the form of the X-ray-like DEXA scan results, which displayed a reduction in the grayish outline representing the fat on my thighs.
But here’s the catch: The central region consisting of my quadriceps and hamstrings did not expand excessively after performing countless squats. In fact, it remained largely the same, which is the main point of this anecdote. If I hadn’t performed those repetitions while following my diet, my muscles would have likely experienced some shrinkage, and this would have affected my metabolism as well.
Having stronger legs may indeed be a secret to maintaining a healthy physique. “When you enhance the power and endurance of your legs, it generally makes exercising and moving around easier, resulting in increased physical activity throughout the day. You burn more calories overall,” explains McCarthy. In fact, a study conducted at the University of Alabama at Birmingham revealed that women who managed to sustain their weight loss one year after dieting exhibited significantly greater leg strength compared to those who did not. (Also: Trainers Recommend Adding These Leg Day Exercises to Your Workouts)
But What About Your Ankles?
The area between your calf muscles and ankles is not defined by muscle but rather by the Achilles tendon, which connects the two. For some individuals, this region narrows significantly due to well-toned calf muscles, while for others it gradually slopes downward. And then there are those whose lower legs appear to have a straight line with no visible indentation at all, leading to the unflattering and body-shaming term: cankles.
“Cankles are essentially a visual illusion,” explains Dr. Wright. “Models often appear to have cankles because their legs are cylindrical from the knee to the ankle. It’s all relative,” she adds. (More importantly, here’s how weak ankles and ankle mobility impact the rest of your body.)
For the calf muscles to appear tapered, they must possess a certain amount of muscle bulk. However, many individuals are hesitant to strengthen their calf muscles due to fear that it will result in thickness and contribute to a cankle-like appearance. “That’s a misconception. Cankles do not arise from muscle because by the time you reach the ankle, it’s all tendons,” explains Dr. Wright. It’s a combination of genetic factors, fat accumulation, and body composition.
Now that you have learned about the appearance and function of leg muscles, let’s delve into a detailed breakdown of the specific leg muscles and their location.
The Structure of Leg Muscles
Refer to the labeled diagrams of leg muscles below for a more comprehensive view of the front, side, and back of your leg muscles.
Front Leg Muscles
Front Leg Muscles
When it comes to the front of your legs, there are two muscle groups — the frontal upper leg muscles (i.e. your thigh) and the frontal lower leg muscles (i.e. your shin). There are four components of your quadriceps: rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. The tibialis anterior is the strip of muscle that makes up your shin and helps you bend your ankle to move your foot toward your knee. The peroneus longus runs down the outside of your frontal lower leg.
Outer Leg Muscles
Your inner leg muscles or inner thigh muscles are referred to as your adductor muscles, which include the pectineus, adductor longus, adductor brevis, and gracilis. This group of leg muscles is responsible for bringing your thigh toward the center of your body, as well as rotating the thigh bone.
Rear Leg Muscles
The posterior leg muscles (below the glutes, at least) are what make up your hamstrings and calves. The three hamstring muscles — biceps femoris, semitendinosus, and semimembranosus — are responsible for bending your knee and extending your hip. The calf muscles include the gastrocnemius, the uppermost of your two that provides your feet with power with each step, and the soleus, which lies underneath the gastrocnemius. The tibialis posterior is a very small muscle deep inside the calf that helps stabilize your foot.